Increased understanding ofthe epigenetic mechanisms that control gene expression programs important for leukemia development and survival provides exciting new opportunities for therapeutic intervention. Specifically, methylation or acetylation of histones maintains gene expression programs necessary for leukemia cell proliferation and survival. The central hypothesis for this project is that small molecule inhibitors of histone modifications will effectively target acute lymphoblastic leukemia (ALL) cells. We will assess this through the use novel small molecules, chemical biological approaches, novel mouse models and genetic screens. In specific aim 1 we will work to define a role for D0T1L inhibition in MLL- Rearranged ALL through characterization of a potent, specific D0T1L inhibitor that has remarkably selective anti-proliferative and proapoptotic effects on MLL-rearranged ALL cells. In aim 2 we will develop assays and use novel chemical approaches for high-throughput identification of new small molecule DOT1L inhibitors. In specific aim 3 we will work with to develop rationale for clinical development of histone deacetylase (HDAC) inhibitors as therapies for ALL, with a particular focus on leukemias that result in high end-induction MRD. We will also determine rational combinations of HDAC inhibitors and proapototic molecules and with ploidy- specific agents, and evaluate specific HDAC1 and HDAC2 inhibitors as potential ALL-directed therapeutics. Based on preclinical data, we will assess HDAC inhibitors in relapsed ALL. We expect these aims to bring new more efficacious, less toxic therapies to children and adults diagnosed with ALL. RELEVANCE (See instmctions): While improvements have been made in the treatment of childhood acute lymphoblastic leukemia (ALL), children diagnosed with ALL harboring MLL-rearrangements continue to do poody. Also, specific subsets of children and most adults diagnosed with ALL continue to have poor outcomes. In this project we will characterize new small molecules that target D0T1L, a histone methyltransferase important for survival of yWLL-rearranged leukemias. We will also assess both pan-histone deacetylase (HDAC) inhibitors and newly developed HDAC1/HDAC2 specific inhibitors as potential therapeutics against ALL cells.